Inspection/Maintenance System Check
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Inspection/Maintenance System Check
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Several states require that a vehicle pass on-board diagnostic (OBD) system tests and the inspection/maintenance (I/M) emission inspection in order to renew license plates. This is done via the status display for the I/M system in the scan tool. Via the scan tool, the technician can check the state of the I/M system and determine whether the car meets with local requirements. While testing in the I/M System Status mode, some DTCs may occur that are called I/M Test DTCs. If an I/M Test DTC is defined as an actual fault code, the MIL lamp will be commanded ON, and the DTC is stored in non-volatile memory. The intended use of this data is to prevent vehicles from passing I/M inspection without proper repair to the vehicle. These fault codes are not erasable from any scan tool command or erasable by disconnecting power to the controller. The I/M Test DTCs will be supported by all emissions related ECUs such as ECMs, TCMs, FPCMs, etc. An I/M Test DTC will not be stored or erased from the ECU except at the end of trip processing which occurs 5 s after ignition OFF.
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Conditions for Updating the I/M System Status
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Each system requires at least one, and sometimes several, diagnostic tests. The results of these tests are reported by a diagnostic trouble code (DTC). A system monitor is complete when either all of the DTCs comprising the monitor have Run and Passed, or any one of the DTCs comprising the monitor have illuminated the malfunction indicator lamp (MIL) . Once all of the tests are completed, the I/M System Status display will indicate YES in the Completed column.
For example, when the HO2S Heater Status indicates YES, either all of the oxygen sensor heater tests have passed or one of the tests has illuminated the MIL. If the vehicle has four heated oxygen sensors, either all four heater circuit tests have passed or one of the heater circuit tests has illuminated the MIL. The I/M System Status will indicate NO under the Completed column when any of the required tests for that system have not run. The following is a list of conditions that would set the I/M System Status indicator to NO:
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The vehicle is new from the factory and has not yet been driven through the necessary drive conditions to complete the tests.
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The battery has been disconnected or discharged below operating voltage.
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The control module power or ground has been interrupted.
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The control module has been reprogrammed.
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The control module DTCs have been cleared as part of a service procedure.
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Conditions for Clearing I/M Test DTCs
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Only the OBD II System can erase the I/M Test DTC. The OBD II system must determine that the malfunction that caused the I/M Test DTC to be stored is no longer present and is not commanding the MIL. Each of the following represents ways to clear an I/M Test DTC:
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If the MIL goes out due to 3 passing drive cycles, scan tool code clear is not used, the I/M Test DTC is erased at power down of the last drive cycle.
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If a scan tool code clear is used to turn OFF the MIL, the I/M Test DTC is not erased. The DTC must PASS and not FAIL. The I/M Test DTC is erased at power down of the drive cycle.
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If the controller is reflashed/reprogrammed, all I/M Test DTCs are erased.
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For the OBD II System to run a single drive cycle for clearing an I/M Test DTC, all of the following conditions must occur:
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Cumulative time of engine run time is greater than 600 s.
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Cumulative vehicle operation above 41 km/h (25 mph) for over 300 s.
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Continuous vehicle idle for greater than 30 s.
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Turn ignition OFF for 5 s and allow the code to clear.
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Monitored Emission Control Systems
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The OBD II system monitors all emission control systems that are on-board. Not all vehicles need every possible emission control system. For example, a vehicle may not be equipped with secondary air injection (AIR) or exhaust gas recirculation (EGR). The OBD II regulations require monitoring of the following; if equipped:
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The air conditioning system
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The catalytic converter efficiency
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Comprehensive component monitoring-Emission related inputs and outputs
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The evaporative emission (EVAP) system
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The fuel delivery system
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Heated catalyst monitoring
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The oxygen sensor system (O2S or HO2S)
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The oxygen sensor heater system (HO2S heater)
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For the specific DTCs required for each system, refer to
Inspection/Maintenance (I/M) Test DTC Table
. Systems such as misfire and comprehensive components may not be listed in a system status list. These tests run continuously and do not require an I/M System Status indicator.
The I/M System Status display provides an indication of when the control module has completed the required tests. This does not necessarily mean that the test has passed, only that a decision was made. If the diagnostic fails, a DTC will indicate the failure. If a failure indication is present for a DTC associated with one of the I/M regulated systems, it may prevent other required tests from running. For example, a DTC for the control circuit of the EVAP purge solenoid may not be listed in the Inspection/Maintenance System DTC Table because it is a continuous test. If this DTC is set, the Active Tests for the EVAP system may not run.
The I/M System Status information may be useful for a technician to determine if diagnostics have run when verifying repairs.
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Circuit/System Verification
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Review the I/M System Status indicators. All I/M System Status indicators should report YES, and no I/M Test DTCs should be present.
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1.
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Note
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Many DTC related repairs will instruct the technician to clear the DTC information. Clearing the DTC will reset the I/M System Status indicators to NO. Performing the I/M Complete System Set Procedure will set each of the I/M System Status indicators to YES.
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Observe the Engine DTC information with a scan tool. Verify no DTCs are present.
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Review applicable service bulletins for software updates that would prevent the I/M System Status tests from completing.
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Observe the I/M System Status indicators.
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Observe the I/M Test DTC information with a scan tool. Verify there are no I/M Test DTCs present.
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If an I/M test DTC is set and all of the I/M system status indicators are YES there is no need to perform the complete system set procedure. Diagnose the DTC using the
Diagnostic trouble code DTC list - vehicle
and refer to Conditions for clearing the I/M test DTCs.
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